Deflectable loop electrode array mapping and ablation catheter for cardiac chambers

ABSTRACT

A cardiac arrhythmia mapping and ablation catheter has a main catheter that is provided with a mapping and ablation system attached to its distal end which includes an adjustable loop carrying an electrode array including a plurality of parallel-connected, separately operable mapping/ablation electrodes in conductive relation to the external environment and arranged in spaced serial relation along the loop. Insulated conductors connect the electrodes electrically with an input/output device outside the catheter for mapping the electrical activity of the chamber wall contacted and ablating tissue as indicated. Drawstring control wires are used to control the size, shape and deflection or posture of the loop. A distal extension may optionally be provided to adapt the loop specifically to addressing the tricuspid annulus. A fixed version is also disclosed.

BACKGROUND OF THE INVENTION

I. Cross-Reference to Related Application

This patent application is a continuation-in-part of copendingapplication Ser. No. 07/840,162, filed Feb. 24, 1992 now abandoned.

Reference is made to applications Ser. Nos. 07/835,553 and 07/840,026 ofcommon inventorship. Both of these cross-referenced applications alsoare directed to improved catheters.

II. Field of the Invention

The present invention is directed generally to an improved catheter forus in the field of cardiac arrhythmia ablation. More particularly, theinvention is directed to the use of a deflectable, preferably size andshape adjustable, electrode array loop catheter which allows theoperator to rapidly map heart chambers and including the tricuspidannulus and ablate the desired tissue using the same mapping electrodein the array that is positioned on or near the site that should beablated.

III. Discussion of the Related Art

Normal cardiac pacing, in a healthy heart, is controlled by a specialstructure known as the sinoatrial node (SA node). This is the naturalpacemaker of the heart and is a specialized tissue located within themuscle walls of the right atrium. The SA node provides impulses whichdominate the inherent or natural rhythmic contractions of the heartatria and the ventricles. This dominance or control involves thetransmission of ionic impulses through cardiac conduction pathways inthe atria and the ventricles which cause the heart to contract and relaxin an orderly sequence at a rate dictated by the SA node. This sequenceensures that blood flow to the systemic circulation or the pulmonarysystem will be maximized with each ventricular contraction. The SA nodehas its own inherent rate which can be modified by signals from thenervous system. In response to excitement, physical activity, etc., thesympathetic and parasympathetic nervous systems react to modify therate.

A depolarization impulse begins with the SA node and spreads as anelectrical wave from its location in the right atrium across to the leftatrium and down toward the transition zone between the atrium and theventricles where another node, known as the atrioventricular (A-V) nodeor junction, is located. This impulse conducts through the A-V node in aslower fashion and continues to a common pathway known as the bundle ofHis between the right and left ventricles, then into multiple pathscalled right and left bundle branches, each bundle branch supplying oneventricle. These bundle branches then divide into an extensive networkof finer paths of conducting tissue which spread from the inner to theouter surfaces of the heart and which are referred to as the Purkinjefibers. These fibers feed the depolarization impulse into all portionsof the ventricular myocardium.

As long as this system is intact, impulses are transmitted normally andcardiac rhythm is maintained. The natural impulse or current flow in thecardiac conduction system, however, may be interrupted or altered bycongenital defect, disease or injury which can cause the formation ofscar tissue. When a sufficiently severe injury or a congenital defect ispresent in the cardiac conductive pathways or in the ventricularmyocardium, the electrical impulses are not transmitted normally andrhythmic disturbances known as cardiac arrhythmias can occur. Withrespect to such disturbances, the term bradycardia is used to describean abnormal slowing of the cardiac contractions and the term tachycardiais used to describe abnormally rapid heart action. While either of theseconditions can endanger the life of the patient, tachycardia is the moreserious, particularly in patients having underlying heart disease.

Ventricular tachycardia and other ventricular arrhythmias have beentreated with a number of drugs such as lidocaine, quinidine andprocainamide. In cases of excessive sympathetic nervous activity oradrenal secretion, Beta blocking drugs have been used. In cases wheredrug therapy has been ineffective in preventing tachyarrhythmias,certain surgical procedures have been used to ablate the arrhythmogenictissue either from the atrium or the ventricles. This procedure involvesextensive surgery in which an incision through the pericardium and heartmuscle is made locate the arrhythmogenic tissue, which is then frozen orsurgically removed to be replaced by scar tissue.

Because open-heart surgery is a high risk procedure which requires aprolonged period of hospitalization and recuperation, a less traumaticsolution is needed. In response, catheters of various types have beendevised and used for diagnosing and treating a number of cardiacabnormalities to avoid the trauma of open-heart surgery. For example, asa method for resolving atherosclerotic plaque build up, stenotic lesionsare now routinely opened by the use of balloon angioplasty. In thisprocedure, a balloon carrying catheter is navigated through thepatient's vascular system to the location of the stenosis. The balloonis inflated by fluid injected through a lumen of the catheter to applypressure to the walls of the clogged vessel, thereby opening it.

Catheter devices have also been used to locate and ablate cardiacconduction pathways. One such device is shown in U.S. Pat. No. 4 785815, in which a catheter tube carries at its distal end at least oneelectrode for sensing membrane potentials within the heart, togetherwith a heating device for ablating at least a portion of the pathwaylocated by the sensing device. Another thermal ablation catheter formicrotransection or macrotransection of conduction pathways within theheart, which uses a resistive heating element at its distal end forhighly localized treatment, is illustrated and described in U.S. Pat.No. 4 869 248. These devices are generally effective once the ablatingelement is properly positioned at the localized area of interest. Acatheter device of the class described has also been developed whichemploys a single handle operated deflection wire. Such a device isdisclosed in U.S. Pat. No. 4 960 134.

Most present cardiac tissue ablation procedures involve the use of radiofrequency (RF) electrical current transmitted to the tissue via acatheter which is positioned as closely as possible to thearrhythmogenic site within the atria or ventricles. Radio frequencyelectrical current heats the tissue surrounding the catheter, creating adiscrete, dense lesion. In order for the patient to be cured of thearrhythmia, the lesion must be created in the area from which thearrhythmia originates. Improvement in the maneuverability of suchdevices and the accessibility of them to areas difficult to reach butwhich are common sources of abnormal rhythm would greatly assistoptimization of arrhythmia location and precise positioning of thecatheter prior to ablation.

In many patients with cardiac arrhythmias, the tissue that causes theabnormal rhythm is located in the right side upper chamber (atrium) ator near the tricuspid ring. The most appropriate location for ablationis defined by mapping a large area of tissue in order to identify theearliest electrical activity. The mapping process and the identificationof the anatomical location of the catheter is at times a challenging andlaborious procedure which as a result subjects the operator and patientto prolonged x-ray radiation.

Unlike with procedures for ablation of tissues around the mitral valveannulus, where a coronary sinus catheter readily provides crucialinformation as to the location of the arrhythmogenic tissue and alsoserves as a guide to the placement of the ablation catheter, no suchstructure is present at the right side of the heart around the tricuspidvalve. A device which provided both the ability to rapidly map theentire tricuspid ring and areas adjacent to it, as well as the abilityto apply the ablation energy to the most desirable location using thesame catheter would not only expedite the ablation procedure, but alsomake it easier and more effective.

SUMMARY OF THE INVENTION

The present invention provides an unique mapping and ablation catheterdevice that provides both the ability to rapidly map cardiac chambersand also the entire tricuspid ring and areas adjacent to it, as well asthe ability to apply the ablation energy to the most desirable locationusing the same catheter. This capability makes it easier to map the areaof interest, and expedites and makes the ablation procedure moreeffective. The present invention is a new catheter design whichincorporates a distal loop segment that can be opened and closed bytensing drawstring wires extending from the catheter handle. In oneapplication, the loop is of a size designed to fit around the tricuspidvalve. The most distal part of the loop may be provided with anextension in the form of a short length of flexible polyurethane tubingthat can be inserted into the most anterior angle of the tricuspid ring.Without the extension, the device is suitable for mapping any othercardiac areas. While dimensions are not critical, the extension isnormally about 4 French in diameter and less than an inch (18 mm) long.The loop extension provides an anchor for the loop at its distal end andthe catheter shaft, from which the loop extends, is designed to beadvanced into the inferior vena cava and provide the anchor for the loopat its proximal end.

The loop is equipped with a pair of arrays of serially distributedelectrodes spaced apart and connected in a manner to allow recordingfrom any location in the loop or around the tricuspid ring. In onearrangement, each electrode back side is shaved or flattened to permitthe majority of the exposed surface to be in contact with the tissue andnot with the blood. In one embodiment, the electrodes had a length ofabout 4 mm and were spaced about 2 mm apart. The system contains twodeflection wires that are threaded in opposed relation along oppositesides of the loop arc extending thorough the loop and the main catheterlumen to the handle which control the size and shape of the loop. Inthis configuration, when these control wires are in their normal(untensioned) state, the loop remains closed with the opposite sides ofthe loop arc substantially parallel. Similar amounts of tension appliedto both wires causes the loop to open symmetrically and remain in aconstant position corresponding to the tensions applied; however, thepulling or tensing of but a single wire causes the loop to openasymmetrically and deflect toward the side of the loop arc opposite thatbeing deflected. The loop is further mounted on a rigid sheath of strongthermoplastic material which is capable of sustaining the high pullforces on the deflection wires without damage, as well as maintaining apredetermined shape modified by heating the shaft and bending asrequired for the particular procedure. Once the thermoplastic cathetershaft is cooled, the angulation which was applied to the catheter duringheating will be maintained. This construction enables the operator torotate the catheter loop and control the location of the tip in a morepositive manner.

The predetermined selected shape of the shaft allows the operator toadvance the catheter loop sheath carrying the loop more readily into thetricuspid ring from the inferior vena cava. The configuration is suchthat rotation of the shaft causes the loop to rotate along the axis ofthe tricuspid ring, which allows the operator to map atrial andventricular electrical activity at the posterior and anterior aspect ofthe tricuspid ring. The operator can readily change the catheterdeflection by applying tension on one of the pull wires to change theloop angle with respect to the catheter shaft, thus providing greaterflexibility of angles and shapes to accommodate the varying anatomicalpositions of the tricuspid ring.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, wherein like numerals are utilized to designate likeparts throughout the same:

FIG. 1A is a greatly enlarged schematic view of the electrode array loopof the invention;

FIG. 1B is a cross-section view along lines 1B--1B of FIG. 1A;

FIGS. 2A-2E are schematic views of the electrode array loop in a varietyof dispositions and degrees of openness;

FIGS. 3A and 3B are schematic side and top views, broken, and partiallyin section, with parts cut away of a catheter and handle for use withthe electrode array;

FIG. 4 is a schematic top view, broken, partially in section, with partscut away of a catheter and handle for use with the electrode array;

FIG. 5 is a greatly enlarged exploded plan view of parts of the handleof FIGS. 3A, 3B and 4; and

FIGS. 6A-6D are schematic views of the electrode array loop showing avariety of deflection dispositions.

DETAILED DESCRIPTION

The invention will next be described with reference to the several viewsof the drawings. The loop shown generally at 20 in the enlargedschematic view of FIG. 1A is made of thick but flexible reinforcedpolymer tubing (typically 1.7 mm in diameter) which is configured toform an ellipse when opened. The loop of polymer tubing, in thisembodiment, is provided with a distal extension or appendage 22 also ofa compatible polymeric material such as polyurethane. By way of example,the extension 22 may be 18 mm long by 4 French in diameter. The loop 20also includes a pair of deflectio control wires 24 and 26 each anchoredto the distal portion of the respective half of the tubular ellipticalloops 28 and 30 by respective T-shaped pins 32 and 34. The furthercontains a series of spaced tubular noble metal electrodes shown in partat 36 on either half of the elliptical loop which are further attachedto individual respective insulated conductor wires as at 25 and 27 whichmay be bundled as represented by 38 and 40. Both the deflection controlwires 24 and 26 and the conductors 38 and 40 are threaded through therespective loop lumen and the main catheter sheath to the controlhandle. The deflection control wires 24 and 26 thread through individualcarrier tubes 46 and 48, respectively.

As better seen in FIG. 2A, when the loop is fully closed, it forms asubstantially straight line. While dimensions are not critical, thelength of the long axis is typically about 6 cm and the loop extensionsegment 22 about 18 mm. The electrodes 36 are preferably made ofplatinum tubing 2 mm thick and 4 mm long.

Prior to securing the electrodes, each of the platinum tubing segments36 is attached to a respective low resistance conductor wire as at 25and 27 nominally 0.08 mm in diameter that are threaded through smallholes in the tubing (not shown). Each set of conductor wires 38, 40 isinserted into a polymer, preferably polytetrafluoroethylene (PTFE), tubeas at 42, 44 that is disposed inside and extends the length of the maincatheter shaft 18. This protects the conductor wires and carries them toan electrical connector which is mounted on a short cable on theproximal end of the catheter handle (FIGS. 3A and 3B).

The tubular electrodes are also illustrated in FIGS. 6A-6C where a fullview of the tubular segments is shown at 136. The electrodes 136 arelikewise attached to individual respective insulated conductor wiresshown bundled at 138 and 140 carried in tubes 142 and 144, respectively,in FIG. 6D. As with the electrodes 36, the electrodes 136 are typically4-5 mm in length with any sharp edges removed and are separated by gaps137 which may be any desired length but are typically about 2 mm. Thecontrol wire carrier tubes 146 and 148, respectively, carry controlwires 124 and 126 as illustrated in the embodiment of FIGS. 1A and 1B.Control of individual electrodes for mapping activity and for ablationis the same as that of FIGS. 1A-1B and 2A-2E.

Regardless of electrode configuration, the main catheter shaft 18, then,contains four PTFE tubes, as shown in FIG. 1B, tube 42 carries thebundle of electrical conductor wires from the side 30 of the electrodeson the loop 20, 44 carries the bundle of electrical conductor wires fromthe side 28 of the electrodes on the loop 20. Tube 46 carries the pullwire 24 for the deflection of the lower loop segment 28 and 48 carriesthe pull wire 26 for the deflection of the loop segment 30. Thedeflection wires 24, 26 are preferably stainless steel, nominally 0.22mm thick and attached to the T-shaped pins 32 and 34 (FIG. 1A) bycrimping the respective pin onto the wire. The T-shaped pin and the pullwire are inserted into the loop tubing through a small hole in the inneraspect of the loop tubing. Each T-shaped pin may be imbedded into thetubing and secured with a compatible adhesive such as polyurethane glue.

As shown in FIGS. 2A-2E, when tension is applied to the deflection wires24, 26, the upper and lower segments 28 and 30 will bend to form theloop which will result in the loop opening (2C). When the wire 26 ispulled alone or to a greater degree, the loop will open and deflectdownward as shown in FIG. 2D. The reverse occurs when the lower wire 24is pulled as illustrated in FIG. 2E.

In FIG. 6D, control wires 124 and 126 are shown offset with respect tothe conductor bundles 138 and 140 as opposed to the essentially in-lineconfiguration of FIG. 1B, which is parallel to the plane of theundeflected electrode loop in its normal position parallel to the maincatheter segment 18. The essentially 90° offset arrangement shownrepresents an exaggerated illustration pertaining to the use of thecontrol wires for side-to-side deflection of the loop as shown in FIGS.6B and 6C. Even with the in-line arrangement of FIGS. 1A and 1B, someside-to-side loop deflection control can be accomplished in addition tothe loop shape control; and, it will be appreciated that any desireddegree of offset, symmetrical or asymmetrical, can be employed.

Although dimensions are not critical, the distal portion of the mainshaft 18 of the catheter is preferably about 8F in diameter and made ofa reinforced thermosetting polymer tubing that can be reshaped byheating. The tubing is designed to be heated and shaped prior to use.Once cooled, the new shape is maintained with minimal deflection of theshaft even when high tension is applied to the loop deflection controlor pull wires.

The construction of the proximal end of and control handle elements forthe catheter of the invention is illustrated in FIGS. 3-5. FIGS. 3A and3B show the top and side view of the handle 50, generally. The cathetersheath 18 fits into the handle and the two bundles of electrical wirescontaining conductors connecting each electrode on the loop are threadedthrough the catheter tube segment 52 into and through the length of thehandle to the proximal end of the handle 20 where they connect to amulti-pin input/output connector 54.

The two pull wires are attached to separate pull wire tension controlsystems and shown in greater detail in FIGS. 4 and 5. As seen in theexploded view of FIG. 5, the tension control systems and handle assemblyinclude a pair of spaced symmetrical handle mechanisms. The tensioncontrol systems are shown in the form of opposite hand releasableratchet mechanisms in which a pair of tension control lever members 64and 66 with respective finger operated handle segments 68 and 70 areattached to hollow, generally cylindrical ratchet members 72 and 74 asby set screws 76 and 78. The ratchet members 72 and 74 have respectivesets of unidirectionally engaging gear teeth 82 and 84 designed tocooperate with a resilient engaging and release mechanism which includesa pair of oppositely disposed locking members having shafts 86 and 88,designed to be journaled in bores 90 and 92 and having sets of gearteeth 94 and 96 disposed to mesh with respective teeth sets 82 and 84 asthe locking members are urged outward by a spring member 98. As can bestbe seen in FIG. 5, the ratchet members 72 and 74 are provided withchannels as at 100 and 102 which are designed to accommodate lockingpins 104 when the tension control system is assembled in a handle bore104 (FIG. 4).

As shown in FIG. 4, the loop deflection control wires 24 and 26 arethreaded through openings 110 and 112 and attached to the ratchetmembers 72 and 74 and wound around them. Movement of the tension controllever handles 68 and 70 toward the proximal end of the handle draws thewires 24 and 26 and causes the loop to open. Each lever maintains itsposition upon release using the spring loaded gear tooth locking systemwhich are caused to be continually engaged by the spring member 98.Rotation of the members 86 and 88 is prevented by two teeth 106 and 108,respectively, on each locking member that engage channels 103 (FIG. 4)in the handle member 50. Since each lever can be moved independently ofthe other, the deflection of the loop can be skewed or biased andthereby adjusted to better fit any shape of any chamber addressed. Thetension on the deflection control wires is relieved individually bysimply pushing in on the release knob ends of the members 86 and 88 todisengage the gear teeth and release the deflection control ratchetcylinder, allowing the corresponding handle to move back toward theclosed loop position. To deflect or open the loop, the deflectioncontrol handle of interest can be moved without pressing the lockingcontrol knob, since the one-way locking teeth sets 82, 94 and 84, 96slide on each other as a ratchet mechanism in one direction.

In operation, the catheter system is introduced by an incision into thevascular system of the patient and routed through the vascular systeminto the inferior vena cava such that the distal end of the maincatheter extends into the right atrium chamber of the patient's heart.Once the proper position is reached, reciprocal movement of the handles68 and 70 produces precise control of the size and shape of the loop 20such that any point on the wall of the valve is readily accessible tothe electrodes 36 of the ring 20. The distal tip of the catheter mayalso be extended through the tricuspid valve into the right ventricle toaddress the ventricular side of the tricuspid valve with the loop 20.The electrode members 36 can be utilized to map the cardiacdepolarization potentials throughout the valve folds and surfaces,thereby locating and mapping any early activation sites. The tipextension is used to stabilize the loop location for mapping and fortissue ablation.

The ease and precision of the mapping made possible with the cathetersystem of the invention makes location of early activation sites andablation of associated tissue with respect to the tricuspid valve areamuch easier and more precise. This makes the procedure much morepractical than previous systems.

This invention has been described herein in considerable detail in orderto comply with the Pat. No. Statutes and to provide those skilled in theart with the information needed to apply the novel principles and toconstruct and use embodiments of the example as required. However, it isto be understood that the invention can be carried out by specificallydifferent devices and that various modifications can be accomplishedwithout departing from the scope of the invention itself. For example,the loop can be made to conform to a fixed predetermined shape such as afully open loop upon being deployed as it emerges from the catheterlumen. Memoried materials such as flexible but memoried plastics, ormetallic materials such as a nickel titanium alloy commonly known asnitinol, can be employed in such an embodiment.

I claim:
 1. A cardiac arrhythmia mapping and ablation cathetercomprising:a main catheter comprising an elongated, flexible plastictube having a proximal end and a distal end, and an outside diametersmall enough to pass through a vascular systems from an introducer siteinto a desired cardiac chamber and having the capability required tonegotiate the vascular system, the main catheter further describing amain internal lumen extending from the proximal end to the distal end; amapping and ablation system attached to the distal end of the tube ofthe main catheter and further including,a distal adjustable tublar loophaving generally oppositely disposed sections and carrying an electrodearray including a plurality of externally conductive, individuallyconnected mapping/ablation electrodes arranged in spaced serial relationalong the adjustable tubular loop, insulated conductor means connectingthe individual electrodes electrically with an input/output deviceoutside the catheter for mapping electrical activity of a chamber wallcontacted and ablating tissue as indicated, loop control means foradjusting and controlling shape and posture or deflection of theadjustable array loop comprising a pair of tension control members, eachassociated with a section of the adjustable tubular distal loop to applya desired amount of tension or provide slack.
 2. The cardiac arrhythmiaablation catheter of claim 1 wherein the pair of tension control memberscomprises a pair of tensioning drawstring wires.
 3. The cardiacarrhythmia ablation catheter of claim 1 wherein the loop control meansfurther comprises means for separately controlling the tension appliedby each tension control member.
 4. The cardiac arrhythmia ablationcatheter of claim 1 wherein the tension control members are at leastslightly offset with respect to a plane parallel to a plane described bythe electrode array loop in an undeflected state to increase leveragerelative to side-to-side deflection control of the loop itself.
 5. Thecardiac arrhythmia ablation catheter of claim 1 wherein the pair oftension control members are symmetrically placed with respect tocontrolling the shape and posture of the adjustable array loop such thateach addresses a section of equal length in the loop.
 6. The cardiacarrhythmia ablation catheter of claim 1 wherein the main catheterfurther comprises:control handle means for controlling the mapping andablation system connected to the proximal end of the main catheter; apair of tension control means in the catheter handle means, each one ofthe pair of tension control means being associated with a correspondingone of the pair of tension control members, for separately controllingtension in the corresponding one of the pair of tension control members;and wherein the pair of tension control members are threaded in opposedrelation along opposite sides of the loop and extend through the loopand the main catheter lumen and including means separately connectingeach tension control member to a corresponding tension control means,each tension control member thereby controlling tension in therespective connected side of the loop.
 7. The cardiac arrhythmiaablation catheter of claim 6 wherein each one of the pair of tensioncontrol means further comprises hand-operable releasable ratchetmechanism having tension control lever member attached to rotate agenerally cylindrical adjustable tension controlling ratchet member towhich the corresponding tension control means is fixed thereby causingthe corresponding tension control means to wind and unwind andaccordingly to apply tension to and relax an affected portion of theloop.
 8. The cardiac arrhythmia ablation catheter of claim 7 wherein thetension control means further comprise resilient release means forindividually disengaging each ratchet member to thereby release tensionon a corresponding tension control member.
 9. The cardiac arrhythmiaablation catheter of claim 6 wherein the pair of tension control membersare symmetrically placed with respect to controlling shape and postureof the adjustable array loop such that each addresses a section of equallength in the loop.
 10. The cardiac arrhythmia ablation catheter ofclaim 9 wherein the loop has a distal extremity and further comprises alength of flexible tubing extending from the distal extremity of theloop to aid in positioning the loop as for use at a tricuspid valve. 11.The cardiac arrhythmic ablation catheter of claim 10 wherein the lengthof flexible tubing is an extension of the loop.
 12. The cardiacarrhythmia ablation catheter of claim 1 wherein the electrodes of theelectrode array are raised and have exposed outer surfaces directed awayfrom the loop which are substantially flattened to present a largerelectrode contact surface to tissue contacted which is situatedgenerally perpendicular to a plane described by the loop.
 13. Thecardiac arrhythmia ablation catheter of claim 1 wherein the electrodesof the electrode array are substantially tubular.
 14. The cardiacarrhythmia ablation catheter of claim 1 wherein the elongated tube ofthe main catheter has a tube wall that is further characterized byhaving a segment thereof extending to the distal end, having athermoplastic nature providing the ability to be heated and formed in ashape as desired, such formed shape being retained upon cooling.
 15. Thecardiac arrhythmia ablation catheter of claim 1 wherein the loop has adistal extremity and further comprises a length of flexible tubingextending the distal extremity of the loop to aid in positioning theloop as for use at a tricuspid valve.
 16. A cardiac arrhythmia ablationcatheter comprising:a main catheter comprising an elongated, flexibleplastic tube having a proximal end and a distal end, and an outsidediameter small enough to pass through a vascular system from anintroducer site into a desired cardiac chamber, the main catheterfurther describing a main lumen extending from the proximal end to thedistal end, the main catheter having the capability required to enablerouting through the vascular system; a mapping and ablation systemattached to the distal end of the tube of the main catheter and furthercomprising, an adjustable tubular distal electrode array loop havinggenerally oppositely disposed sides configured to address a tricuspidannulus carrying an electrode array including a plurality of externallyconductive, individually connected mapping/ablation electrodes arrangedin serial spaced relation along the adjustable tubular loop, insulatedconductor means connecting the electrodes electrically with oneinput/output device outside the catheter for mapping electrical activityof a chamber wall contacted and ablating tissue as indicated, a pair oftensioning drawstring wires for adjusting and controlling shape andposture of the adjustable array loop; control handle means forcontrolling the mapping and ablation system connected to the proximalend of the main catheter; a pair of tension control means in the controlhandle means for separately controlling tension in each drawstring wireof the pair; and wherein the pair of drawstring wires are threaded inopposed relation along the oppositely disposed sides of the loop andextend through the loop and the main catheter lumen and are eachconnected separately to a respective one of the pair of tension controlmeans.
 17. The cardiac arrhythmia ablation catheter of claim 16 furthercomprising a short length of flexible tubing extending the distal end ofthe loop to aid in positioning the loop for use at a tricuspid valve.18. The cardiac arrhythmia ablation catheter of claim 16 wherein thetensioning drawstring wires are at least slightly offset with respect toa plane parallel to a plane described by the electrode array loop in anundeflected state to increase relative side-to-side deflection controlof the loop itself.
 19. The cardiac arrhythmia ablation catheter ofclaim 16 wherein the pair of tensioning drawstring wires aresymmetrically placed with respect to controlling shape and posture ofthe adjustable array loop such that each addresses an equal section ofthe loop.
 20. The cardiac arrhythmia ablation catheter of claim 16wherein the electrodes of the electrode array are raised and haveexposed outer surfaces directed away from the loop which aresubstantially flattened to present a larger electrode contact surface totissue contacted which is situated generally perpendicular to a planedescribed by the loop.
 21. The cardiac arrhythmia ablation catheter ofclaim 16 wherein the electrodes of the electrode array are substantiallytubular.
 22. A method of mapping and ablating tissue in a cardiacchamber of interest comprising the steps of:introducing a cardiacmapping and ablation catheter system into a vascular system at anintroducer site, the catheter system having,a main catheter comprisingan elongated, flexible plastic tube having aproximal end and a distalend, and an outside diameter small enough to pass through the vascularsystem from an introducer site into a cardiac chamber of interest andhaving the capability required to enable routing of the main catheterthrough the vascular system, the main catheter further describing maininternal lumen of a relatively large size extending from the proximalend to the distal end; a mapping and ablation catheter system attachedto the distal end of the main catheter and further comprising,anadjustable tubular distal loop having generally oppositely disposedsides carrying an electrode array including a plurality of externallyconductive, individually connected mapping/ablation electrodes arrangedin spaced relation along the adjustable distal loop, insulated conductormeans connecting each electrode electrically with an input/output deviceoutside the catheter for mapping electrical activity of a chamber wallcontacted and ablating tissue as indicated, and control means foradjusting and controlling shape and posture or deflection of theadjustable array loop comprising a pair of tension control members eachassociated with a side of the adjustable tubular distal loop to apply anamount of tension or slack thereto as desired; navigating the maincatheter system along in a vascular system from an introducer site toaccess a heart chamber of interest and inserting the mapping andablation catheter system into the chamber of interest; using the pair oftension control members, each connected to one of the pair of tensioncontrol members to adjust an associated side of the adjustable tubulardistal loop and loop deflection to conform to a shape of inner wall inthe chamber of interest as required and using the electrodes to mapelectrical activity thereof; using the electrodes of the tubular loop toablate sites of early activity as required.
 23. The method of claim 22wherein the mapping and ablation catheter system further comprises:athermoplastic distal segment in the main catheter connecting theadjustable tubular distal loop; and wherein the method further comprisesthe step of using heat to shape the thermoplastic distal segment of themain catheter as required to allow the loop to address an interior wallin the chamber of interest.
 24. The method of claim 22wherein theadjustable distal tubular loop has a distal extremity; and wherein themapping and ablation catheter system further comprises a short tubularextension of a distal extremity of the loop to aid in positioning theloop for use at a tricuspid valve; and wherein the method furthercomprises the step of:inserting the tubular extension into a mostanterior angle of a tricuspid ring; and using the control means toadjust the posture and shape of the loop to conform to an inner wall andmap and ablate as needed.